The present invention relates to the field of optical sensor systems that employ the detection of interference-induced phase differences resulting from the operation of a physical parameter to be measured on an optical sensor. More specifically, the present invention relates to a coherent fiber-optic system employing a Fabry-Perot pressure sensor to measure pressures (such as those resulting from the propagation of an acoustic wave through a medium) with a high degree of accuracy and reliability under adverse environmental conditions.
Coherent fiber-optic systems for the sensing and measurement of physical parameters are well-known in the art. See, for example, U.S. Pat. No. 5,200,795--Kim et al. Many of these prior art systems are plagued by one or more problems, such as high cost, insufficient accuracy, and poor-reliability under adverse conditions.
One type of system that has shown promise in overcoming such problems is that which employs miniature silicon Fabry-Perot pressure sensors, of the type described in Halg, "A Silicon Pressure Sensor with an Interferometric Optical Readout", 1991 International Conference on Solid State Sensors and Actuators, IEEE Catalogue No. 91CH2817-5, pp. 682-684 (1991). A system employing such a sensor is described in Bush et al., "Low Cost Optic Interferometric Microphones and Hydrophones", SPIE Vol. 2292, Fiber Optic and Laser Sensors XII, pp. 83-93 (1994). The system contemplated by Bush et al. would employ two or more steady-state LED's, emitting different wavelengths, as the optical signal sources. It is believed that, in practice, this approach may yield less than optimal results in terms of stability and accuracy, due to, for example, instabilities in the output of the LED's. In addition, the mechanism for demodulating the pressure-modulated optical signal may a be amenable to further simplification and cost reduction.
It would therefore be advantageous to provide an optical pressure sensor system, employing Fabry-Perot sensors, that is low-cost, and highly accurate, stable, and reliable, even in an adverse operational environment.